The UOA is telling us that, despite the heavily predominant "city" driving, everything is fine:
Wear incredibly low.
Contamination nearly non-existent.
TBN strong; vis perfectly in place; FP nice and high.
This UOA is yet more proof that "severe service factors" really are not severe at all, in reality. If this "severe" service of city stop/go driving is so horrid, then by all means, someone step forward and show me the consequences! Because unless you're blind, there's nothing whatsoever to be concerned about here and everything points to extending the OCIs. 10k miles would be a MINIMUM for me under these conditions. I like your plan; extend out a little at a time. To be honest, I see no reason you cannot jump right to 15k miles and then UOA, but I realize many would cringe at such an adventure, so taking a methodical build up approach is perfectly acceptable.
WHEN YOU PAY FOR DATA, DON'T IGNORE WHAT IT TELLS YOU! I am amazed at the nay-Sayers that often will ignore the reality of the data, preferring to stick with hype and rhetoric. And that's OK for them, but shame be upon your oily head for trying to convince others that incredibly excellent UOAs such as this one should be ignored, all for the sake of "cheap insurance" of frequent OCIs.
If one does not want to utilize facts, that's fine. But don't eschew others that actually THINK their way into a maintenance program, rather than "feel" an arbitrary OCI limit.
For goodness sake, how much more-extra-super-duper-better does a UOA have to be before some of you will actually begin to see the light? This engine is running 1ppm/1k miles for Fe, and the other metals are so low they are just noise. No - I change my statement; the other metals are so low they are only echos of distant noise! I swear some of you would still recommend an OCI if there were nothing but zeros for wear metals. Because it would be "cheap insurance" in case a particle of metal actually made it's way loose. What a bunch of fear mongers some of you are!
Rummy has the right approach here. Run; test; analyze; re-assess. Repeat as necessary.
Kudos to you for your great engine and methodical work.